A review on the removal of conditioning chemicals from cooling tower water in constructed wetlands

Large volumes of freshwater are used globally for cooling towers. The reuse of discharged cooling tower water in cooling towers itself could mitigate freshwater scarcity problems. Prior to its reuse, the cooling tower blowdown has to be desalinated. However, physicochemical desalination techniques are hampered by conditioning chemicals (CC) that are added to the cooling tower water circuit to prevent corrosion, mineral scaling, and biofouling and can damage physicochemical desalination equipment. The potential of constructed wetlands (CWs) for the cost-effective removal of these CC prior to desalination is discussed in this review. The characteristics of CWs that determine their suitability for the removal of CC from cooling tower blowdown are elucidated, such as multiple removal pathways working simultaneously. In addition, specific challenges for the design of a constructed wetland for cooling tower blowdown treatment are reviewed, such as configuration options, the toxicity of CC, and the formation and removal of harmful byproducts.